Prior known signal generators provided output signals at a different frequency from the input frequency by dividing the input and output down to a common frequency with frequency dividers and comparing the resultant common frequency signals. The resolution of these signal generators is limited by the common frequency.
One signal generator that offsets frequency offsets phase by changing the frequency over a selected time interval has the disadvantage that the frequency and phase offsetting of this device is not independent and phase offsetting is not instantaneous.
Direct digital synthesizers have been used to phase shift signals. Japanese Patent Application/Public Disclosure Document No. 4-229703 shows a method of generating waveforms with a direct digital synthesizer (DDS). Ikuzawa, U.S. Pat. No. 5,517,156, shows a digital phase shifter using a DDS.
Look-up tables in memory have been used to phase shift signals. Takahashi, U.S. Pat. No. 5,732,109, and Treise et al., U.S. Pat. No. 4,484,296 show examples of waveform table look-up memories in variable phase generators and phase detectors. The use of look-up tables is limited in the resolution or increment size by the available memory for the tables.